MEMS based current sensor using magnetic-to-mechanical conversion and reference components

ABSTRACT

A micro-electromechanical system (MEMS) current sensor is described as including a first conductor, a magnetic field shaping component for shaping a magnetic field produced by a current in the first conductor, and a MEMS-based magnetic field sensing component including a magneto-MEMS component for sensing the shaped magnetic field and, in response thereto, providing an indication of the current in the first conductor. A method for sensing a current using MEMS is also described as including shaping a magnetic field produced with a current in a first conductor, sensing the shaped magnetic field with a MEMS-based magnetic field sensing component having a magneto-MEMS component magnetic field sensing circuit, and providing an indication of the current in the first conductor.

RELATED APPLICATIONS

The present application is a Divisional of application Ser. No.10/863,442, filed Jun. 7, 2004, and issued as U.S. Pat. No. 7,112,951 onSep. 26, 2006, which is herein incorporated by reference.

BACKGROUND

The present disclosure relates generally to the field of electricalcurrent sensing devices. More particularly, the present disclosurerelates to a micro-electromechanical system (MEMS) based current sensorusing a force acting between current carrying conductors and a mutuallyinductive coupling.

Sensors for sensing a current based on the force between two currentconductors are known in the art. It is known that a current carryingconductor produces a magnetic field in the vicinity of the currentcarrying conductor. It is also known that the magnetic field produced bythe current carrying conductor can induce a force with another currentcarrying conductor disposed in the magnetic field produced by thatcurrent carrying conductor. While such known current sensors are capableof detecting currents in the “macro world”, they are not suitable forsensing currents in the nanotechnology scale environment of mechanicaland electromechanical devices produced by micromachining processes.

Additionally, such known current sensors have several disadvantages. Ingeneral, the physical and electrical operating characteristics of suchknown current sensors are not compatible with sensing currents in thenanotechnology scale environment. The physical dimensions of thesecurrent sensors are one barrier. The electrical operatingcharacteristics also prove disadvantageous in that a magnetic fieldproduced by a current carrying conductor and sensed by the macro-sizedcurrent sensor tends to vary across the area of the sensor. Thisintroduces an error that must be compensated for in order to achieveaccurate current measurements. Also, known current sensors areindividually fabricated and packaged devices dedicated to performing asingle function in the process of current sensing. Each of theseattributes adds cost and application limitations of the current sensor.Further, the macro-sized current sensors tend to produce heat, therebyreducing the efficiency of the current sensors and introducing apossible error factor to the accuracy of the current sensor.

Thus, there exists a need in the art for a MEMS-based current sensorusing the force between current carrying conductors and a mutuallyinductive coupling that overcomes one or more of the aforementioneddeficiencies of known current sensors using the force between currentcarrying conductors.

SUMMARY

In one exemplary embodiment, there is provided a micro-electromechanicalsystem (MEMS) current sensor including a magnetic field shapingcomponent for shaping a magnetic field produced by a current in a firstconductor, and a MEMS-based magnetic field sensing component having amagneto-MEMS component for sensing the shaped magnetic field and, inresponse thereto, providing an indication of the current in the firstconductor.

In another exemplary embodiment, there is provided a method of sensing acurrent using a micro-electromechanical system (MEMS) comprising shapinga magnetic field produced by a current in a first conductor, and sensingthe shaped magnetic field by a MEMS-based magnetic field sensingcomponent having a magneto-MEMS component magnetic field sensing circuitfor sensing the shaped magnetic field and, in response thereto,providing an indication of the current in the first conductor.

DRAWINGS

FIG. 1 is a schematic diagram representative of a MEMS-based currentsensor constructed in accordance with an embodiment of the invention.

FIG. 2( a) is an exemplary depiction of the MEMS-based current sensorand current carrying conductor of FIG. 1.

FIGS. 2( b)-(c) are exemplary depictions of the MEMS-based currentsensor of FIG. 1.

FIGS. 3( a)-(c) are exemplary depictions of the MEMS-based currentsensor of FIG. 1.

FIGS. 4( a) and (b) illustrate a MEMS based current sensor constructedin accordance with another embodiment of the invention.

FIGS. 5( a) and (b) are exemplary depictions of magnetic field shapingin accordance with another embodiment of the invention.

DETAILED DESCRIPTION

With reference to FIG. 1, there is shown a schematic diagramrepresentative of a MEMS-based current sensor in accordance with thedisclosure herein, generally represented by reference numeral 100. TheMEMS-based current sensor 100 uses, for example, a force between currentcarrying conductors, a mutual inductance induced between terminals of asecond conductor in a magnetic field, to sense (i.e., detect) anddetermine characteristics (e.g., magnitude and direction) of a current Iin a first current carrying conductor. In case the terminals of thisconductor are shorted together, this mutually inductive coupling resultsin a back electromotive force due to the Lenz law. In general, themethod of sensing the current in the first current carrying conductorincludes a process of magnetic field shaping by a magnetic field shapingcomponent 5 and a process of magnetic field sensing by a magnetic fieldsensing component 25. The magnetic field shaping component 5, and inparticular a magnetic field-to-magnetic flux density converter 15thereof, may be implemented using MEMS devices. The magnetic fieldsensing component 25 is preferably implemented using MEMS devices toprovide a current sensor that is highly accurate, reliable, robust, andintroducing little to no error to the current being sensed.

The size of the MEMS current sensor 100 facilitates the sensing ofcurrents in applications where space is limited. The use of MEMS-basedcomponents contributes to the reliability of the current sensor 100.Due, at least in part, to the non-contact sensing methods of sensingcurrent using MEMS current sensors 100, the MEMS current sensor 100preferably has no impact on the magnitude and/or direction of thecurrent being sensed. For example, sensing current using the MEMScurrent sensor 100 preferably introduces very little (i.e., preferablynegligible) error into the current being sensed. Given the dimensions ofMEMS-based components and the sensitivity of the same, the MEMS currentsensor 100 preferably does not introduce or cause any appreciablevariation or change in the current being sensed or measured. Moreover,the MEMS current sensor 100 is advantageous for its reduced cost andsignificantly reduced size. Further, due to micro-lithography andmicro-fabrication techniques, the fabrication of the MEMS current sensor100 is advantaged through increased accuracy and precision.

The MEMS-based current sensor 100 operates to sense and determine thecurrent in a first conductor by making use of either the force actingbetween, a conductor carrying an unknown current and a reference currentpositioned in the magnetic field produced by the unknown currentcarrying conductor or the mutual inductance induced between terminals ofa reference conductor. It is known that a current carrying conductorgenerates a magnetic field in the vicinity of the current carryingconductor. It is also known that a current carrying conductor placed inthe magnetic field generated by a first current carrying conductor willhave a force acting on it proportional to the current in the firstcurrent carrying conductor. Accordingly, it is possible to sense acurrent carrying conductor without having to make physical contact withthe current carrying conductor. It is similarly known that a secondconductor placed in the magnetic field generated by the first currentcarrying conductor will have a mutual induction generated betweenterminals of the second conductor as governed by the Lenz law.Accordingly, since the magnetic flux due to the first conductor variesin time, there will be a voltage induced between terminals of the secondconductor that is proportional to the time rate of change of the flux.Alternatively, if the terminals of the second conductor are shorted,there will be a back electromotive force acting on the second conductordue to mutually inductive coupling.

There may be a number of forces that act on current carrying conductors.These forces include a Lorentz force generated between the two currentcarrying conductors, and a mutual inductance generated by a secondconductor due to the time rate of change of the magnetic flux due to oneof the current carrying conductors. The characteristics of each of thesetypes of known electromagnetic ways of inducing a change based in amagneto-MEMS component can be used in accordance with the disclosureherewith to provide the MEMS-based current sensor 100.

Referring to FIG. 1, the magnetic field shaping component 5 shapes amagnetic field produced by a current I flowing in a first conductor. Thecurrent I flowing in the first conductor is the current being sensed,detected, and preferably quantified. The process of shaping current Iincludes providing the detected current I in a form that is suitable foruse by the other components of the MEMS-based current sensor 100.Depending on the particular implementation of the other componentsinterfaced with the magnetic field shaping component 5, the magneticfield shaping component 5 can include a current-to-magnetic-field (H)converter 10 and a magnetic-field-to-magnetic flux density (B) converter15. The process of shaping current I includes providing the firstconductor that the detected current I flows through in a form that issuitable for use by the other components of the MEMS-based currentsensor 100. The process of shaping current I also includes shaping theconductor through which the detected current I flows in a form toprovide a magnetic field that is uniform in magnitude and/or direction.The shaping of the current carrying conductor may be done to render thedetection of the magnetic field more suitable for use by the othercomponents of the MEMS-based current sensor 100. That is, the shaping ofthe current carrying conductor can be used to effectuate the magneticfield shaping of magnetic field shaping component 5.

The electric current carrying conductor is surrounded by a magneticfield as a consequence of the electric current flowing therein. Themagnetic field is a vector quantity, i.e., it has a direction and amagnitude. The current-to-magnetic field converter 10 shapes themagnetic field, H (20), such that it is shaped into a usable andreliable vector field in space for use by the other components of theMEMS based current sensor 100. The magnetic field-to-magnetic fluxconverter 15 converts the magnetic field produced by the electriccurrent flowing in the first conductor to a corresponding magnetic fluxdensity, B (22), of the electric current such that it is shaped into ausable and reliable magnetic flux density vector field for use by theother components of the MEMS-based current sensor 100.

In one aspect, the magnetic field shaping component 5 can include eitherthe current-to-magnetic-field converter 10 or themagnetic-field-to-magnetic flux density converter 15, or both. Themagnetic field shaping component 5 provides a shaped magnetic field 20and/or a magnetic flux density 22 corresponding to the current I beingsensed. In one aspect, the current-to-magnetic-field converter 10 andthe magnetic-field-to-magnetic flux density converter 15 provide ashaped magnetic field 20 and a shaped magnetic flux density 22,respectively, corresponding to the current I being sensed concurrentlywith each other.

The current-to-magnetic-field converter 10 and the magneticfield-to-magnetic flux density converter 15 may or may not be discretedevices. That is, they may be provided in a single device. Also, thecurrent carrying conductor itself may be shaped to at least contributeto the shaping of the magnetic field. Thus, in one aspect, the magneticfield shaping component 5 may be implemented by configuring thegeometric shape of the conductor carrying the current being sensed toshape the magnetic field produced thereby.

Referring to FIG. 5( a), the magnetic field 20 generated by a currentcarrying conductor 4 carrying a current I has a generally square “U”shape and a generally rectangular cross-section. The contributions frombranches 4 a-4 c add to generate a magnetic field that is generallyshaped to be uniform in direction and magnitude. In addition, themagnetic field and flux density at the apex of the inside of thisrectangular-shaped conductor 4 is larger in magnitude than thecorresponding values that would be generated by a straight conductorB_(single). As illustrated, the corresponding values would be2.3×B_(single) and 1.6×B_(single), respectively. This illustrates howthe current-to-magnetic field converter provides a function of shaping ageometric property of the first conductor 4, shapes a geometric propertyof at least a branch of the first conductor 4, and assigns a geometricalrelationship of the first conductor 4 with respect to at least a branchof the first conductor 4. In another embodiment, the conductor 4 can bedivided into two branches as illustrated in FIG. 5( b). A slot iscreated by respective branches 4 a and 4 b of the conductor 4,respectively carrying current components Ia and Ib in two substantiallyparallel paths. In yet another embodiment, an additional fluxconcentrator may be used as part of the magnetic field-to-magnetic fluxconverter 15. This flux magnetic flux concentrator includes a highmagnetic permeability material disposed and shaped to conformsubstantially to a magnetic property of the conduct such as the magneticfield created by the currents I, Ia, and Ib.

The shaped magnetic field 20 and/or the magnetic flux density 22corresponding to the current I being sensed is passed to the MEMS-basedmagnetic field sensing component 25, as illustrated by the arrow betweenthe magnetic shaping component 5 and the MEMS-based magnetic fieldsensing component 25 (FIG. 1). The MEMS-based magnetic field sensingcomponent 25 senses the shaped magnetic field 20 and/or the shapedmagnetic flux density 22. In response to the sensing of the shapedmagnetic field 20 and/or the shaped magnetic flux 22, the MEMS-basedmagnetic field sensing component 25 provides an indication of thecurrent in the first conductor. Preferably, the sensed current indicatorincludes both a magnitude and direction component regarding the currentbeing sensed. The sensed current indicator is preferably an electricalindication of the sensed current I.

The illustrated MEMS-based magnetic field sensing component 25 includesa magneto-MEMS component 30 that, among other things, senses the shapedmagnetic field and, in response thereto, converts the sensed shapedmagnetic field 20 and the shaped magnetic flux density 22 to themechanical indicator of the sensed current I. The MEMS-based magneticfield sensing component 25 also includes a compensator 55 for enhancinga function of the MEMS-based magnetic field sensing component 25, and anoutput component 70 for providing an output indicative of the current Iin the first conductor. Output from the output component 70 ispreferably an electrical signal indicative and representative of themagnitude and sign of the current I flowing in the first conductor.

Each of the magnetic field shaping component 5 and the MEMS-basedmagnetic field sensing component 25 includes other components forcarrying out the intended functionality thereof. For example, theillustrated magneto-MEMS component 30 includes a magnetic-to-mechanicalconverter 35 for converting the magnetic representation of the current I(e.g., the shaped magnetic field 20 and the shaped magnetic flux density22) to a mechanical change, and a structural component 40 for providinga structural support and for being responsive to the mechanical changeand providing an indication of the mechanical force. The magneto-MEMScomponent 30 also includes a mechanical sense component 45 for sensingthe mechanical indication provided by structural component 40, and areference component 50 for providing a reference indicator for themechanical indication to the structural component 40.

In one aspect, the shaping of the magnetic flux density may beaccomplished by using a flux concentrator to obtain a usable andreliable signal representative of the current that can be processed asneeded to make an accurate determination of the current being sensed.For example, in one embodiment, the flux concentration can be obtainedby using a high permeability material that permits an increasedconcentration of magnetic flux density therethrough.

The mechanical indicator may be the movement of a structural componentthat registers, moves, or otherwise indicates the sensing of themagnetic field. In one embodiment, the mechanical indicator is aninduced stress on the structural component. In yet another embodiment,the mechanical indicator includes modification of a mechanical propertyof the structural component 40, such as, for example, the springconstant and the mass thereof. The modification of the mechanicalproperty of the structural component 40 will result in the modificationof a characteristic response of the structural component 40. Forexample, changing the spring constant or weight of the structuralcomponent 40 causes the response of the structural component 40, forexample, a deflection or compression of the structural component, toaccordingly change. The resonance frequency, for example, can be alteredby the modification of the mechanical property. Thus, monitoring anddetecting the variance in the response of the structural component 40(e.g., resonance frequency) can be used to detect/determine a change inthe mechanical property of the structural component 40, caused by themechanical indicator from the magnetic-to-mechanical converter 35corresponding to the current being sensed by the current sensor 100.

The structural component 40 may be a membrane, a cantilever, a bridge,or any number of other structural devices. The mechanical indicatorprovided by the structural component 40 conveys the vector space valueof the mechanical indicator, including one or more of an associatedamplitude, direction, speed, and any other characteristic thereof thatcan be used to convey the vector space value of the mechanicalindicator. The mechanical indicator is sensed at the mechanical sensecomponent 45. The sensed mechanical indicator is converted to aninterface signal that can be used to further process, interpret, and/orcommunicate the current sensed by using the generated magnetic field. Amechanical-to-electrical converter 75 of an output component 70 takesthe interface signal of the mechanical indicator and converts it to ausable electrical signal for interpretation and/or further processing.

The magneto-MEMS component 30 may include a compensator 55. Thecompensator 55 preferably includes an excitation means or source 60 anda controller 65. The excitation means 60 provides excitation quanta(i.e., an amount of excitation energy) for use by the MEMS currentsensor 100. The controller 65 controls, for example, a switching and anapplication of the excitation quanta of the excitation means 60 and thereference signal of the reference component 50. In another embodiment,the controller selects between differing values of the excitation quantaand a plurality of reference components 50.

The magneto-MEMS component 30 can include the output component 70. Theoutput component 70 preferably has a mechanical change to themechanical-to-electrical converter 75 and an output stage 80. Themechanical change to the mechanical-to-electrical converter 75 receivesthe mechanical indication provided by the mechanical sense component 45and, in turn, provides an electrical indication representative of thesensed current I to output stage 80. The mechanical change to themechanical-to-electrical converter 75 may be based on, for example, ametal strain element, a piezoresistive element, a piezoelectric element,a capacitive element, a tunneling element, or an optical element. Outputstage 80 may interface with a memory, an indicator (e.g., a displayscreen), and/or another device or apparatus for further processing(e.g., a digital signal processor or computer-based analyzer).

In one aspect, the MEMS-based current sensor 100 providesmulti-directional magnetic field sensing. This aspect of the currentsensor can be realized by taking advantage of the degrees of freedomoffered by MEMS and the micro machining and micro-lithographymanufacturing process used therein. Referring to FIGS. 2( a)-(c), thereis shown an exemplary MEMS device for detecting a current in a firstcurrent carrying conductor (not shown). The unknown current beingmeasured in the first current carrying conductor is coupled to apredetermined bias current 190 (i.e., reference signal) controlled toflow in coil 105 and a predetermined bias current 200 controlled to flowin coil 205. The direction of current flow in each of the coils 105 and205 is indicated by the directional arrows associated with the biascurrent 190 and the bias current 200. The coil 105 is supported atcertain points thereon by supports 110, and the coil 205 is supported atcertain points thereon by supports 210. At a cavity 115, the coil 105 isexposed for coupling to the unknown current being measured in the firstcurrent carrying conductor. In the cavity 115, a membrane, for example,is deflected (mechanically moved) in response to, for example, theLorentz force acting between the reference current carrying coil 105 andthe unknown current in the first current carrying conductor, the mutualinductance between a first current carrying coil and the coils 105 and205, and/or by moving a coil in the magnetic field generated by thecurrent in the first current carrying conductor.

Given the geometrical configuration of the coil 105 and the cavity 115as shown, allowing for the coupling of the current carrying conductorsin only the specified cavity 115, and the direction of the bias current190, the Lorentz force in the cavity 115 will act to move a mechanicalMEMS device in the cavity 115 in a direction as indicated by arrow 120(FIG. 2( c)).

While discussed primarily in the context of using the Lorentz forcebetween the first and the coil (i.e., second) conductors, themagnetic-to-mechanical converter 35 can be modified to use mutualinductance, a moving loop and a magnetic field generated by the firstcurrent carrying conductor. Additionally, other characteristicrelationships may be used to derive a mechanical indicator of themechanical indicator corresponding to the current being sensed.

As illustrated in FIG. 2( b), the coil 205 forms a flexure and issupported at certain points thereon by supports 210. At the cavity 115,the coil 205 is exposed for coupling to the unknown current beingmeasured in the first current carrying conductor. In the cavity 115, aMEMS device membrane, for example, is deflected (mechanically moved) inresponse to the Lorentz force acting between the current carrying coil205 and the unknown current in the first current carrying conductor.Given the configuration of the coil 205, the cavity 115 allowing for thecoupling of the current carrying conductors in only the cavity 115, andthe direction of the bias current 200, the force in the cavity 115 willact to move a mechanical MEMS device in a direction as indicated by anarrow 220.

Using micro-machining and micro-lithography manufacturing processes,exemplary coils 105 and 205 may be constructed in separate layers ofconductive metal and insulating layers of material to provide a singleMEMS-based current sensor that uses the force between current carryingconductors to sense an unknown current flowing in a first conductor.Thus, as demonstrated herein, multiple functions may be accomplished andutilized by the MEMS-based current sensor in accordance with the presentdisclosure. Also, the coils of FIGS. 2( b) and 2(c) may be combined toform the MEMS structure of FIG. 2( a). In this manner, a single MEMScurrent sensor device may be used to detect and sense currents ofvarious directions, magnitudes, and with varying degrees of sensitivity.

In FIG. 2( c), for example, the mechanical-to-electrical converter 75 isshown at the anchor points 110 of coil 105 and the structural support40. At one anchor point 110, a piezoresistor may be used to detect themagnitude of deflection of the cantilevered coils 105. The amount ofstress placed on the piezoresistor is preferably proportional to theamount of deflection experienced by the deflectable membrane and themagnitude of the current flowing in the first conductor. The sidewallsand/or floor of the cavity 115 may be used to detect mechanical changesto the MEMS current sensor as a result of the force exerted thereon bythe current being sensed. For example, electrodes, optical sensors,pressure sensors, and other MEMS-based structures may be used to detectthe mechanical change(s) caused by the current in the first conductor.The mechanical-to-electrical converter may include a resistiveWheatstone bridge and a capacitive Wheatstone bridge as part of theoutput component 70.

The mechanical indicator may be the movement of a structural component40 that registers, moves, or otherwise indicates the sensing of themagnetic field. The structural component 40 may be a membrane, acantilever, a bridge, or any number of other structural devices. Thedetection of the mechanical indicator conveys the actuation of themechanical indicator, including at least one of an associated amplitude,direction, speed, and any other characteristic thereof that can be usedto convey the scope of the mechanical indicator. In one embodiment, thestructural component 40 includes at least one from a group consisting ofa membrane, a cantilever, a deflectable membrane, a diaphragm, a flexuremember, a cavity, a surface micro-machined structure, a comb structure,and a bridge. The mechanical indicator is sensed at the mechanical sensecomponent 45. The sensed mechanical indicator is converted to aninterface signal that can be used to further process, interpret, and/orcommunicate the current sensed by using the generated magnetic field.The mechanical-to-electrical converter 75 of an output component 70takes the interface signal of the mechanical indicator and converts itto a usable electrical signal for interpretation and/or furtherprocessing.

There is shown in FIGS. 3( a)-(c) an exemplary implementation of theMEMS current sensor hereof. As shown, a deflectable membrane 46 issupported over the cavity 115 by structural supports 40. Located on topof and supported by the deflectable membrane 46 in the cavity region ofthe illustrated MEMS structure is a conductor configured as a coil 35.At a base (i.e., floor) of the cavity region, there is a metalconductive bottom electrode.

A number of exemplary excitation sources 60 are shown in FIG. 3( c) forthe MEMS current sensor. For example, a battery 601 and an A-Cexcitation source 602 are depicted. The depicted micro-controller 65 maybe used to control the application of the excitation source from thebattery 601 and/or the AC source 602 to the MEMS-based magnetic fieldsensing component 25, as discussed in regards to FIG. 1. Thus, dependingon, for example, the application or context in which the current isbeing measured and/or the implementation of the magnetic field shapingcomponent 5 and the magneto-MEMS component 30, the excitation source 60can be a DC voltage, an AC voltage, or other excitation quanta. Any oneor more of the excitation sources 60 may be used in accordance with theMEMS current sensor 100. The excitation source may be, for example, acurrent source, a voltage source, a resonance generator, or a groundingreference point.

In one aspect, the switch (SW) 604 of FIG. 3 is connected to ground, andthe coil 35 effectively forms a loop. The thus formed loop may becoupled to a current carrying first conductor, where the current in thefirst conductor is the current being sensed by the MEMS current sensor100. The current in the first conductor (i.e., being sensed) produces amagnetic field in the coil 35 loop; however, there is no voltageproduced in the coil 35 so long as the magnetic flux is not changing.The magnetic field may be changed (i.e., varied) by, for example, movingthe coil 35 into and out of the magnetic field of the first conductor toobtain a time varying magnetic flux. The magnetic field also may bechanged by controlling the switching of a reference signal by themicro-controller 65. The mutual inductance between the two loops,established by virtue of the loop coupled to the varying magnetic field,may be used derive the current in the first current carrying conductorfrom the voltage produced as a result of the mutual inductance betweenthe two conductor loops.

In another aspect, when the magneto-MEMS component 30 is in the vicinityof a current carrying conductor and a current is flowing in the coil 35,the magnetic field generated by the first conductor will exert a force(e.g., Lorentz force) on the magnetic-to-mechanical converter 35, thecoil conductor located atop the membrane. The detected magnetic forceexerts a force on the coil 35 that can move the coil 35. Hence, amagnetic-to-mechanical conversion of the detected magnetic field occurs.As shown in FIG. 3( b), the membrane 46 may be deflected downward into acavity formed by the membrane 46, the support structure 40, and the topand bottom electrodes. The top and bottom electrodes act as themechanical sense component 45 by sensing the mechanical indication ofthe magnetic field generated by the current being sensed. The top andbottom electrodes operate as, for example, a capacitor. Due to thevariance in the distance between the top (coil) and the bottomelectrode, the magnitude and direction of the current being sensed maybe determined.

The mechanical sense component 45 may be, for example, a capacitor, apiezoresistor, or an optical sensor. Based on a mechanical change, thecapacitor, piezoresistor, and optical sensor can be used to detect andprovide an indication of a mechanical change. Placing a stress on thepiezoresistor will change the resistance thereof. Changing the energyexposure of the optical sensor will change a state of the opticalsensor, thereby allowing the optical sensor to signal a mechanicalchange.

A transducer may be used to implement the mechanical sense component 45to provide an indicator of a detectable measurand (e.g., change indistance between top and bottom electrodes) induced by themagnetic-to-mechanical converter 35 (e.g., the deflectable membrane).The transducer may be used to convert a mechanical measurand (e.g., adisplacement, a vibration, a stress, a strain, a torsional stress, amoment, a deflection, a rotation, an elongation, a compression, etc.)into another form or type of signal (e.g., electrical—a current orvoltage, a pressure, or an optical signal, etc.), that is more readilyor conveniently used for further processing and/or output purposes.

As illustrated in FIGS. 4( a) and 4(b), an exemplary MEMS device 300 isplaced in the vicinity of a first conductor 4, in the magnetic fieldgenerated by a current I flowing therein. The MEMS device 300 isillustrative, and not limiting, of the types of MEMS devices applicablewith the disclosure herein. That is, the particular MEMS device 300shown in FIGS. 4( a) and 4(b) is but one example of the many possibleMEMS devices suitable for use in the MEMS based current sensor of thepresent disclosure.

The MEMS device 300 includes a second conductor 315. In one embodiment,the second conductor 315 is a coil, similar to themagnetic-to-mechanical converter 35 (FIG. 1) disposed on top of amicro-mechanical structure 320. The micro-mechanical structure 320 is,in the illustrated example, a cantilever having a free end and asupported end.

The coil 315 is connected to an excitation source 325, for example, acurrent source. The excitation source 325 is preferably controllable bya compensator having a controller (not shown). The controllerpreferably, at least, controls the application and/or selection ofexcitation source(s) 325. The controller may be, for example, a switch,an analog processor, a digital signal processor, a digital computingdevice or an analog-computing device. In the present example, thecontroller controls at least an on, off, and a value of a bias current330 supplied to the coil 315.

A reference component may be included for enhancing a function of theMEMS current sensor. For example, a switch may be included foractivating, processing, and controlling logic functions associated withthe MEMS current sensor. Other functions, such as, balancing andexciting the MEMS current sensor can be provided by a compensator.

The coil 315, based on its configuration, bias current 330, and beingdisposed in the magnetic field generated by the current I, acts to shapethe magnetic field generated by the current I. In particular, themagnetic field generated by the current I is acted upon and influencedby the bias current 330 supplied to the coil 315. The Lorentz force, dueto the interaction of magnetic fields generated by the current I in thefirst conductor 4 and the bias current 330 in the coil 315, causes amechanical action in the MEMS device 300.

Depending on its polarity, the Lorentz force acts to deflect thecantilever 320 at the free end and supported end thereof in a directionindicated by an arrow 340. Since the cantilever 320 is supported at oneend, the free end is free to move up or down in response to the Lorentzforce acting thereon. The support for the cantilever 320 is located tocounteract (i.e., nullify) any deflecting forces acting on the supportedend of the cantilever 320. The induced Lorentz force acts along theshort ends of the coil 315 (i.e., the ends nearer the free and supportedends of the cantilever 320) based on the geometric configuration of thecoil 315 and the bias current. The supported end of the cantilever 320has a mechanical sense component (not shown) located thereon for sensingthe mechanical movement of the cantilever 320. In the example shown, forexample, a piezoresistor may be connected to the cantilever 320 to sensethe movement thereof that, in turn, imparts a stress on thepiezoresistor. The stress on the piezoresistor affects the resistancevalue of the piezoresistor. The changing resistance of the piezoresistorcan be used by the output component 70 to convert from a mechanical toan electrical change, and thus determine the value of the current beingsensed.

The amplitude and direction of the deflection (mechanical action)experienced by the cantilever 320 is proportional to the current I andits polarity. Therefore, the current I flowing in the first currentconductor 4 can be sensed. In another embodiment, a third currentcarrying conductor 316 (FIG. 4( b)) is used to obtain a force balance,active sensing, zero balance sensing, and an equilibrium condition.

As disclosed herein, the need to physically contact a first currentcarrying conductor 4 to sense the current I is obviated. It is alsonoted that due to the small dimensions of micro-machined MEMS device300, the MEMS-based current sensor 100 is itself a dimensionally smalldevice. Accordingly, the change in the magnetic field being sensed bythe MEMS-based current sensor 100 at various points on the sensor isvery small. The MEMS-based current sensor 100 is therefore accuratesince there is no need to compensate for variances across the measuringsensor itself.

In another aspect, due to batch manufacturing techniques ofmicro-machining and the cost efficiencies therein, the MEMS-basedcurrent sensor 100 in accordance with the disclosure herein can bemanufactured in large batches using micro-machining processes, such as,for example, photo lithography and etching. The manufacture of 10 or1000 current sensors can be realized for a small increase in cost. Also,more than one MEMS device may be manufactured per MEMS-based sensor 100.As noted above, the MEMS device of FIG. 3 is but one example of thecurrent sensors in accordance with the present disclosure. Otherembodiments of the MEMS-based current sensor 100 may include multipleMEMS devices in the current sensor for the purpose of, for example,magnetic field shaping, magnetic field sensing, current valueindicating, and other purposes. In regard to micro-machining techniques,more than one (i.e., multiple) MEMS device can be included in oneMEMS-based sensor 100, thus providing a robust packaging since themultiple MEMS devices may be provided on a common substrate die andpackaged therewith. The need for an external interface(s) between themultiple MEMS devices is avoided.

Due at least in part to the use of MEMS technology, the magnetic forcesrequired to operate the MEMS devices are relatively small. The currentsensor hereof thus tends to generate relatively little heat. This isadvantageous in that there is little heat generated by the currentsensors herein that may introduce an error in the sensing of the currentI.

In one aspect, the bias current 330 can be switched on and off under thecontrol of a user. The bias current 330 may be considered a referencecurrent since its value is known and controllable. As a current having aknown value, the bias current 330 (i.e., the reference current) can beused to compensate for the effects of temperature, aging of the sensor,environmental factors, self-inductance errors, etc. This can beaccomplished by monitoring the state of deflection of the cantilever 320with the bias current 315 on and the bias current 330 off. Thedeflection value obtained when the bias current 330 is off can becompared to the deflection value when the bias current 330 is turned on,for example, by obtaining a ratio of the deflection values of the biascurrent 330 in order to compensate for any cantilever deflecting effectswhen the bias current 330 is off. Thus, the MEMS based current sensor100 can be auto-compensating to account for environmental, temperature,and other effects.

It is noted that the auto-compensating aspects and the mechanicalactuated current sensing discussed herein are not limited to theparticular current sensor of FIG. 4. For example, with reference to FIG.3, there is shown the MEMS device compatible with the MEMS-based currentsensor 100. The MEMS device has a deflectable membrane 46 that can beused to detect and indicate the value (e.g., amplitude and polarity) ofthe unknown current being measured. The membrane 46 is suspended over acavity that exposes the membrane and the coil being supplied by acontrollable current source to the magnetic field of the conductorhaving the current being sensed flowing therethrough. The currentcarrying conductor or coil coupled, for example capacitively, to thecurrent being measured is disposed on the membrane.

While the MEMS devices of FIGS. 3 and 4 are not the same, thecontrollable bias current and micro-mechanical aspects of the MEMSdevice of FIG. 3 allow it to be auto-compensating. This aspect is not tobe limited to the exemplary MEMS devices discussed in detail herein. TheMEMS-based devices discussed herein may be manufactured using any numberof known micro-machining techniques.

Various actuating MEMS devices and configurations thereof may be used inthe MEMS-based current sensor 100 without departing from the scope andspirit of the present disclosure.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

1. A micro-electromechanical system (MEMS) current sensor, comprising: afirst conductor for measuring a current; a first coil for receiving afirst predetermined bias current coupled to said current; a second coilfor receiving a second predetermined bias current coupled to saidcurrent; and a MEMS-based magnetic field sensing component having amagneto-MEMS component for sensing a shaped magnetic field and, inresponse thereto, providing an indication of said current in said firstconductor.
 2. The MEMS current sensor of claim 1, wherein saidMEMS-based magnetic field sensing component comprises at least one of acompensator for enhancing a function of said MEMS-based magnetic fieldsensing component, and an output component.
 3. The MEMS current sensorof claim 1, wherein said magnetic field shaping component comprises atleast one of a current-to-magnetic field converter and a magneticfield-to-magnetic flux converter.
 4. The MEMS current sensor of claim 1,wherein said magneto-MEMS component comprises a magnetic-to-mechanicalconverter coupled to a structural component for providing a mechanicalindication of said shaped magnetic field.
 5. The MEMS current sensor ofclaim 4, wherein said MEMS-based magnetic field sensing componentfurther comprises a reference component coupled to said structuralcomponent for providing a reference indicator for said mechanicalindication.
 6. The MEMS current sensor of claim 5, wherein saidreference component comprises a current carrying conductor, electricalconductive coil, a magneto-restrictive element, and an elementgenerating a Lorentz Force.